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28 .\" @(#)chmod.2 8.1 (Berkeley) 6/4/93
38 .Nd change mode of file
44 .Fn chmod "const char *path" "mode_t mode"
46 .Fn fchmod "int fd" "mode_t mode"
48 .Fn lchmod "const char *path" "mode_t mode"
50 .Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag"
52 The file permission bits of the file named specified by
54 or referenced by the file descriptor
60 system call verifies that the process owner (user) either owns
69 system call follows symbolic links to operate on the target of the link
70 rather than the link itself.
74 system call is similar to
76 but does not follow symbolic links.
80 is equivalent to either
86 except in the case where
88 specifies a relative path.
89 In this case the file to be changed is determined relative to the directory
90 associated with the file descriptor
92 instead of the current working directory.
95 are constructed by a bitwise-inclusive OR of flags from the following list, defined
98 .Bl -tag -width indent
99 .It Dv AT_SYMLINK_NOFOLLOW
102 names a symbolic link, then the mode of the symbolic link is changed.
103 .It Dv AT_RESOLVE_BENEATH
104 Only walk paths below the directory specified by the
107 See the description of the
108 .Dv O_RESOLVE_BENEATH
115 argument is an empty string, operate on the file or directory
116 referenced by the descriptor
122 operate on the current working directory.
127 is passed the special value
131 parameter, the current working directory is used.
134 is zero, the behavior is identical to a call to
137 A mode is created from
143 .Bd -literal -offset indent -compact
144 #define S_IRWXU 0000700 /* RWX mask for owner */
145 #define S_IRUSR 0000400 /* R for owner */
146 #define S_IWUSR 0000200 /* W for owner */
147 #define S_IXUSR 0000100 /* X for owner */
149 #define S_IRWXG 0000070 /* RWX mask for group */
150 #define S_IRGRP 0000040 /* R for group */
151 #define S_IWGRP 0000020 /* W for group */
152 #define S_IXGRP 0000010 /* X for group */
154 #define S_IRWXO 0000007 /* RWX mask for other */
155 #define S_IROTH 0000004 /* R for other */
156 #define S_IWOTH 0000002 /* W for other */
157 #define S_IXOTH 0000001 /* X for other */
159 #define S_ISUID 0004000 /* set user id on execution */
160 #define S_ISGID 0002000 /* set group id on execution */
161 #define S_ISVTX 0001000 /* sticky bit */
171 VM system totally ignores the sticky bit
174 On UFS-based file systems (FFS, LFS) the sticky
175 bit may only be set upon directories.
179 (the `sticky bit') is set on a directory,
180 an unprivileged user may not delete or rename
181 files of other users in that directory.
182 The sticky bit may be
183 set by any user on a directory which the user owns or has appropriate
185 For more details of the properties of the sticky bit, see
188 If mode ISUID (set UID) is set on a directory,
189 and the MNT_SUIDDIR option was used in the mount of the file system,
190 then the owner of any new files and sub-directories
191 created within this directory are set
192 to be the same as the owner of that directory.
193 If this function is enabled, new directories will inherit
194 the bit from their parents.
195 Execute bits are removed from
196 the file, and it will not be given to root.
197 This behavior does not change the
198 requirements for the user to be allowed to write the file, but only the eventual
199 owner after it has been created.
200 Group inheritance is not affected.
202 This feature is designed for use on fileservers serving PC users via
203 ftp, SAMBA, or netatalk.
204 It provides security holes for shell users and as
205 such should not be used on shell machines, especially on home directories.
206 This option requires the SUIDDIR
207 option in the kernel to work.
208 Only UFS file systems support this option.
209 For more details of the suiddir mount option, see
212 Writing or changing the owner of a file
213 turns off the set-user-id and set-group-id bits
214 unless the user is the super-user.
215 This makes the system somewhat more secure
216 by protecting set-user-id (set-group-id) files
217 from remaining set-user-id (set-group-id) if they are modified,
218 at the expense of a degree of compatibility.
225 will fail and the file mode will be unchanged if:
228 A component of the path prefix is not a directory.
229 .It Bq Er ENAMETOOLONG
230 A component of a pathname exceeded 255 characters,
231 or an entire path name exceeded 1023 characters.
233 The named file does not exist.
235 Search permission is denied for a component of the path prefix.
237 Too many symbolic links were encountered in translating the pathname.
239 The effective user ID does not match the owner of the file and
240 the effective user ID is not the super-user.
242 The effective user ID is not the super-user, the effective user ID do match the
243 owner of the file, but the group ID of the file does not match the effective
244 group ID nor one of the supplementary group IDs.
246 The named file has its immutable or append-only flag set, see the
248 manual page for more information.
250 The named file resides on a read-only file system.
255 points outside the process's allocated address space.
257 An I/O error occurred while reading from or writing to the file system.
259 Corrupted data was detected while reading from the file system.
261 The effective user ID is not the super-user, the mode includes the sticky bit
263 and path does not refer to a directory.
268 system call will fail if:
271 The descriptor is not valid.
276 refers to a socket, not to a file.
278 The file resides on a read-only file system.
280 An I/O error occurred while reading from or writing to the file system.
282 Corrupted data was detected while reading from the file system.
294 argument does not specify an absolute path and the
298 nor a valid file descriptor open for searching.
302 argument is not valid.
306 argument is not an absolute path and
310 nor a file descriptor associated with a directory.
311 .It Bq Er ENOTCAPABLE
314 or contained a ".." component leading to a
315 directory outside of the directory hierarchy specified by
317 and the process is in capability mode or the
318 .Dv AT_RESOLVE_BENEATH
331 system call is expected to conform to
333 except for the return of
337 bit on directories is expected to conform to
341 system call is expected to conform to
350 system call appeared in
354 system call appeared in
358 system call appeared in